IBMN612404GT3B
IBMN612804GT3B
Preliminary
128Mb Double Data Rate Synchronous DRAM
Auto Precharge
Auto Precharge is a feature which performs the same individual-bank precharge function described above,
but without requiring an explicit command. This is accomplished by using A10 to enable Auto Precharge in
conjunction with a specific Read or Write command. A precharge of the bank/row that is addressed with the
Read or Write command is automatically performed upon completion of the Read or Write burst. Auto Pre-
charge is nonpersistent in that it is either enabled or disabled for each individual Read or Write command.
Auto Precharge ensures that the precharge is initiated at the earliest valid stage within a burst. This is deter-
mined as if an explicit Precharge command was issued at the earliest possible time without violating
t
(min). The user must not issue another command to the same bank until the precharge (t ) is com-
RAS
RP
pleted.
The IBM DDR SDRAM devices supports the optional t
lockout feature. This feature allows a Read com-
RAS
mand with Auto Precharge to be issued to a bank that has been activated (opened) but has not yet satisfied
the t (min) specification. The t lockout feature essentially delays the onset of the auto precharge oper-
RAS
RAS
ation until two conditions occur. One, the entire burst length of data has been successfully prefetched from
the memory array; and two, t (min) has been satisfied.
RAS
As a means to specify whether a DDR SDRAM device supports the t
lockout feature, a new parameter
RAS
has been defined, t
(RAS Command to Read Command with Auto Precharge or better stated Bank Acti-
RAP
vate to Read Command with Auto Precharge). For devices that support the t
lockout feature, t
=
RAS
RAP
t
(min). This allows any Read Command (with or without Auto Precharge) to be issued to an open bank
RCD
once t
(min) is satisfied.
RCD
t
Definition
RAP
CL=2, t =10ns
CK
CK
CK
Command
DQ (BL=2)
NOP
NOP
ACT
ACT
NOP
NOP
RD A
RD A
NOP
NOP
NOP
NOP
ACT
ACT
NOP
NOP
NOP
NOP
DQ0
DQ1
t
t
RASmin
RPmin
*
Command
DQ (BL=4)
NOP
NOP
NOP
NOP
NOP
DQ0
DQ1
DQ2
DQ3
t
RPmin
*
Command
DQ (BL=8)
NOP
ACT
NOP
RD A
NOP
NOP
NOP
NOP
ACT
NOP
DQ0
DQ1
DQ2
DQ3
DQ4
DQ5
DQ6
DQ7
t
t
t
RCDmin
RAPmin
RPmin
*
Indicates Auto Precharge begins here
*
The above timing diagrams show the effects of t
for devices that support t
RCD
lockout. In these cases, the Read
RAS
(min) and dataout is available with the shortest latency from the
RAP
with Auto Precharge command (RDA) is issued with t
Bank Activate command (ACT). The internal precharge operation, however, does not begin until after t
(min) is satisfied.
RAS
©IBM Corporation. All rights reserved.
Use is further subject to the provisions at the end of this document.
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